I don't blame Starmer for this - the big swing was due to the Brexit/UKIP vote evaporating and going tory. Plus the turnout was 42% - the politicians and commentators consider this by-election more important than actual Hartlepool residents did. The majority don't care.
I get the feeling half the people of Hartlepool don't know what day it is. However, blame what, who, whatever you like, the change has a massive political impact for the Labour Party. How could they promise voters anything, after Corbyn's never ending, "we'll nationalise this, we'll pay for that, we'll give free the other" knowing fine well it was an impossibility.
A time comes, when things are really bad, the best option is to clear the decks and start again. a bit like Kinnock did with Militant.
Socialism is dead in the water, time to get real.